Abstract:

A method of determining face paper properties of wallboard including
providing a core strength value of the wallboard, determining a required
nail pull value based the wallboard specifications and calculating a face
paper stiffness value based on the provided core strength value and the
determined nail pull value. The method includes displaying the calculated
face paper stiffness value on a display device.

Claims:

1. A method of determining structural parameters of wallboard,
comprising:providing a core strength value of the wallboard;determining a
required nail pull value based on a thickness of the wallboard
type;calculating a face paper stiffness value based on said provided core
strength value and said determined nail pull value; anddisplaying said
calculated face paper stiffness value on a display device.

2. The method of claim 1, further comprising testing the wallboard using
an Applied Testing System universal machine to determine the core
strength value.

3. The method of claim 1, wherein said core strength value is in the
approximate range of 400 to 500 psi.

4. The method of claim 1, wherein calculating said face paper stiffness
value is based on the following equation:Nail Pull
(lbf)=a+[b×(face paper stiffness (kN/m))]+[c×(core
strength (psi))]wherein a=4.2126759, b=0.009490606731 and c=0.092421774.

5. The method of claim 1, further including calculating a face paper
weight by dividing said face paper stiffness value by a Tensile Stiffness
Index Area (TSIA) value.

6. The method of claim 5, further including selecting a type of face paper
based on said calculated face paper weight.

7. The method of claim 5, wherein said TSIA value is measured by an
ultrasonic tensile strength orientation tester.

8. The method of claim 5, wherein said TSIA value is in the approximate
range of 12 to 20 kNm/g.

9. The method of claim 1, further including storing said calculated face
paper stiffness value in a memory.

10. The method of claim 9, wherein said memory includes at least one of: a
read-only memory, a random access memory and a CD ROM.

11. A method of manufacturing wallboard comprising:determining a required
nail pull value based on the wallboard type;providing a core strength
value of the wallboard;determining a face paper stiffness value based on
said determined required nail pull value and said provided core strength
value;determining a face paper weight based on said calculated face paper
stiffness value;selecting a face paper type based on said displayed face
paper weight; andproducing the wallboard based using said selected face
paper type and said provided core strength value.

12. The method of claim 11, wherein determining said face paper stiffness
value is based on the following equation:Nail Pull
(lbf)=a+[b×(face paper stiffness (kN/m))]+[c×(core
strength (psi))]wherein a=4.2126759, b=0.009490606731 and c=0.092421774.

14. The method of claim 13, wherein said TSIA value is measured by an
ultrasonic tensile strength orientation tester.

15. The method of claim 13, wherein said TSIA value is in the approximate
range of 12 to 20 kNm/g.

16. The method of claim 11, which includes storing at least one of said
calculated face paper stiffness value and said calculated face paper
weight in a memory.

17. The method of claim 16, wherein said memory includes at least one of:
a read-only memory, a random access memory and a CD ROM.

18. The method of claim 11, wherein said core strength value is in the
approximate range of 400 to 500 psi.

Description:

FIELD OF THE INVENTION

[0001]This invention relates to composite building panels. More
specifically, it relates to a method for determining structural
parameters of gypsum wallboard.

BACKGROUND OF THE INVENTION

[0002]Composite building panels, such as gypsum wallboard, are well known
for interior wall and ceiling construction. Some of the main advantages
of wallboard over other materials is that wallboard is less expensive, a
fire retardant and easy to work with in construction applications. In
construction, wallboard is typically secured to wood or metal supports of
framed walls and ceilings using fasteners such as nails or screws.
Because wallboard is relatively heavy, it must be strong enough to
prevent the fasteners from pulling through the wallboard and causing the
wallboard to loosen or fall away from the supports.

[0003]Nail pull is an industry measure of the amount of force required for
wallboard to be pulled away from the associated support and over the head
of such a fastener. Preferable nail pull values for wallboard are in the
approximate range of between 65-85 pounds of force. Nail pull is a
measure of a combination of the wallboard core strength, the face paper
strength and the bond between the face paper and the core. Nail pull
tests are performed in accordance with the American Society for Testing
Materials (ASTM) standard C473-00 and utilize a machine that pulls on a
head of a fastener inserted in the wallboard to determine the maximum
force required to pull the fastener head through the wallboard. Because
the nail pull value is an important measure of wallboard strength,
minimum required nail pull values have been established for wallboard.
Accordingly, manufacturers produce wallboard that meets or exceeds the
minimum required nail pull values.

[0004]To ensure that wallboard meets the required nail pull values,
conventional wallboard manufacturers adjust the structural parameters of
the wallboard. Specifically, manufacturers typically adjust the face
paper weight of wallboard having a known core strength value to meet the
required nail pull value. During manufacturing, wallboard is tested to
determine if it meets the required nail pull value. If the tested nail
pull value of the wallboard is less than the required nail pull value,
manufacturers increase the face paper weight on the wallboard. This
process is repeated until the required nail pull value is met.

[0005]Such a process is inaccurate and commonly causes the tested nail
pull values to exceed the required nail pull values due to excess face
paper weight added to the wallboard. Also, the excess face paper adds
weight to wallboard and thereby increases manufacturing and shipping
costs of wallboard. Further, there is the likelihood of wasting time and
material until the desired nail pull values are achieved on the wallboard
production line.

[0006]Thus, there is a need for an improved technique of adjusting
wallboard manufacturing systems to produce wallboard that meets specified
nail pull values.

SUMMARY OF THE INVENTION

[0007]These, and other problems readily identified by those skilled in the
art, are solved by the present method of determining structural
properties of composite building panels such as wallboard.

[0008]The present method is designed for determining structural parameters
of gypsum wallboard prior to manufacturing to reduce manufacturing and
shipping costs as well as significantly reduce manufacturing time.

[0009]More specifically, the present method determines structural
parameters of wallboard and includes providing a core strength value of
the wallboard, determining a required nail pull value and calculating a
face paper stiffness value based on the provided core strength value and
the determined nail pull value. The calculated face paper stiffness value
is displayed on a display device for use by a manufacturer.

[0010]In another embodiment, a method of manufacturing wallboard includes
determining a required nail pull value, providing a core strength value
of the wallboard and determining a face paper stiffness value based on
the required nail pull value and the provided core strength value. The
method includes determining a face paper weight based on the determined
face paper stiffness value, selecting a face paper type based on the
determined face paper weight and producing the wallboard using the
selected face paper type and the provided core strength value.

[0011]Determining the structural parameters prior to manufacturing enables
manufacturers to save significant manufacturing and shipping costs by
eliminating excess face paper weight that is typically added to wallboard
to meet required nail pull values. Additionally, a significant amount of
manufacturing time is saved because less time is needed to test the
manufactured wallboard to determine the face paper weight needed to meet
required nail pull values. Furthermore, the structural integrity and
strength of wallboard is maintained, even though the additional weight
and stress added by the excess face paper is reduced.

DETAILED DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a table illustrating a comparison between measured nail
pull data and predicted nail pull data for the same types of wallboard
using different face papers.

[0013]FIG. 2 is a graph illustrating nail pull as a function of the face
paper stiffness at different core strength values.

[0014]FIG. 3 is a graph illustrating nail pull as a function of the core
strength at different face paper stiffness values.

[0015]FIG. 4 is a graph illustrating the relationship between the face
paper stiffness and the core strength at different required nail pull
values.

[0016]FIG. 5 is a graph illustrating the relationship between the face
paper weight and the Tensile Strength Index Area (TSIA) values needed to
achieve a required nail pull value of 77 lbf at different core
strength values.

[0017]FIG. 6 is a table identifying certain face paper weight values and
Tensile Strength Index Area (TSIA) values needed to achieve a required
nail pull value of 77 lbf at different core strength values based on
the graph of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

[0018]Nail pull values are critical to the strength and usefulness of
gypsum wallboard. If a nail pull value for a particular wallboard is too
low, the fastener holding the wallboard on a frame or other support can
pull through the wallboard and cause the wallboard to crack, break or
fall from the frame or support. Alternatively, if nail pull values are
too high (i.e., significantly exceed required nail pull values),
wallboard production resources are inefficiently applied and money is
wasted during manufacturing.

[0019]A problem in gypsum wallboard manufacturing is how to accurately
determine the face paper weight that correlates to a required nail pull
value for wallboard and a way that more efficiently utilizes
manufacturing and shipping costs, as well as manufacturing time. As
stated above, wallboard manufacturers perform tests on wallboard to
determine if it meets a required nail pull value. If the required nail
pull value is not met, manufacturers typically increase the face paper
weight of the wallboard. These steps are repeated until the required nail
pull value of the wallboard is met. This process is not accurate and
often causes the wallboard to have excess face paper, which increases the
overall weight of wallboard and thereby increases manufacturing and
shipping costs as well as manufacturing time.

[0020]The present method determines a face paper weight, or alternatively
a face paper stiffness value, for wallboard prior to manufacturing that
meets the required nail pull value. The method utilizes the following
equation that correlates a required nail pull value with the face paper
stiffness value and the core strength value of wallboard. The equation is
as follows:

where a=4.2126759, b=0.009490606731, c=0.092421774 are constants
determined from testing data that best fit the data shown in FIG. 1.

[0021]Prior to manufacturing, the core strength value of wallboard is
determined and the required nail pull value is determined for the
wallboard to be manufactured (i.e., quarter inch, half inch, etc.). These
values are entered in Equation (1) above to determine the face paper
stiffness value of the wallboard. For example, the face paper stiffness
value for wallboard having a core strength value of 400 pounds per square
inch (psi) and a required nail pull value of 77 pound-force (lbf) is
as follows:

[0022]The face paper stiffness value is a product of the face paper weight
and the Tensile Stiffness Index Area (TSIA) value as shown in the
following equation:

Face Paper Stiffness (kN/m)=Face Paper Weight (g/m2)×TSIA
(kNm/g) (2)

[0023]Using the above example, the Face Paper Weight for the above
wallboard having a core strength value of 400 psi, a required nail pull
value of 77 lbf and a TSIA of 26 kiloNewton-meter/gram (kNm/g) is as
follows:

[0024]In the above equation, the TSIA value is a measurement of the
normalized face paper stiffness in all directions on the wallboard.
Specifically, an ultrasonic Tensile Stiffness Orientation (TSO®)
tester machine measures the Tensile Stiffness Index (TSI) in all
directions on the wallboard to determine the TSIA. The stiffer the face
paper, the larger the TSIA values. The approximate range of TSIA values
for wallboard is 12 to 20 kNm/g.

[0025]The face paper stiffness value and TSIA value are used to determine
the weight of the face paper that is needed to achieve the required nail
pull value for wallboard having a designated core strength value. The
calculation for determining the face paper weight is therefore a two-step
process of first determining the face paper stiffness and then
determining the face paper weight for the wallboard being manufactured.

[0026]Equations (1) and (2) are preferably stored in a memory of a
computer, personal data assistant or other suitable device. The required
nail pull values, core strength values and constants are also stored in
the memory in a database or other searchable data format. The memory may
be a read-only memory (ROM), random access memory (RAM), compact disk
read-only memory (CD ROM) or any other suitable memory or memory device.
A user or manufacturer inputs the required nail pull value and designated
core strength value for the wallboard into the computer using a keyboard
or other suitable input device. Alternatively, the required nail pull
value and designated core strength value for the wallboard may be
downloaded and stored in a file or folder in the memory. A processor,
such as a microprocessor or a central processing unit (CPU), calculates
the face paper weight for the wallboard using Equations (1) and (2), the
inputted nail pull value and the inputted core strength value. The
calculated face paper weight, or alternatively the face paper stiffness
value, is displayed to a user on a display device such as a computer
screen, monitor or other suitable output device or printed out by a
printer. The user uses the calculated face paper weight to select the
face paper or face paper type that is to be adhered to the core during
manufacturing of the wallboard. The face paper selected using the present
method typically reduces the face paper stiffness and weight needed to
achieve the required nail pull value compared to conventional wallboard
production techniques. Additionally, the present method reduces the
overall weight of the manufactured wallboard, which reduces manufacturing
and shipping costs. The present method also significantly reduces the
manufacturing time associated with producing the wallboard because the
intermediate testing of the wallboard to determine if the wallboard meets
required nail pull values is no longer necessary.

[0027]FIG. 1 is a table that illustrates a comparison between the measured
nail pull data and the predicted nail pull data for different wallboard
(sample nos. 1-11) using Equation (1). As shown in the table, the
predicted average nail pull data using Equation (1) correlates well with
the tested or measured average nail pull data of the wallboard. For
example, the average tested or measured nail pull value for sample no. 4
was 83 compared to the predicted nail pull value of 82 using Equation
(1). Similarly, the tested or measured average nail pull values for
sample no. 5, sample no. 6 and sample no. 11 also differ by a value of
one compared to the corresponding average predicted nail pull value using
Equation (1) (e.g., 82,81; 80,79; 81,80). Furthermore, the predicted nail
pull values for sample no. 8 and sample no. 10 wallboard were exactly the
same as the corresponding tested or measured nail pull values (e.g.,
80,80 and 77,77). Thus, the present method predicts the nail pull values
for wallboard with a high degree of accuracy.

[0028]Equations (1) and (2) can also be used to predict different
structural parameters or values of wallboard to enhance the manufacturing
process.

[0029]For example, from Equation (1), nail pull data can be expressed as a
linear function of the face paper stiffness at different core strength
values ranging from 100 psi to 700 psi, as shown in FIG. 2. The core
strength value of wallboard varies based on the type of wallboard being
manufactured. The typical range of core strength values for the wallboard
considered in FIG. 1 is 400 to 500 psi.

[0030]The nail pull data can also be plotted as a linear function of the
core strength with the face paper stiffness values ranging from 1000 kN/m
to 6000 kN/m, as shown in FIG. 3. Preferably, the face paper stiffness
values range from 2500 to 4000 kN/m for wallboard. In FIGS. 2 and 3, it
is apparent that increasing either the face paper stiffness value or the
core strength value of wallboard increases the nail pull value.

[0031]FIG. 4 shows a plot of the face paper stiffness value as a function
of the core strength value at various different nail pull values.
Specifically, line "A" illustrates the relationship between the face
paper stiffness values and the core strength values at a target minimum
nail pull value of 77 lbf. The ratio of the empirical constants c/b
(=9.74) in Equation (1) provides the change in the face paper stiffness
values with respect to the change in the core strength values. To
maintain the required nail pull value of 77 lbf, a reduction (or
increase) of 100 psi in the core strength values corresponds to a 974
kN/m increase (or decrease) in the face paper stiffness values.
Furthermore using Equation (2), a higher face paper stiffness value can
be accomplished by increasing either the face paper weight or the TSIA.

[0032]FIG. 5 illustrates the relationship between the face paper weight
and the TSIA that meets a required nail pull value of 77 lbf. The
face paper weight requirements for different TSIA values are summarized
in the table shown in FIG. 6. Note that increasing the TSIA value from 14
to 19.5 kNm/g tends to reduce the required face paper weight by an
average of 28%, while maintaining the required nail pull value of 77
lbf.

[0033]The present method enables wallboard manufacturers to determine
important parameters and properties of the wallboard prior to
manufacturing such as the face paper weight needed to achieve a required
nail pull value. Obtaining these parameters prior to manufacturing helps
to significantly reduce manufacturing time, as well as manufacturing
costs and shipping costs. The present method also allows manufacturers to
maintain the structural integrity and performance of wallboard without
adding face paper weight on wallboard.

[0034]While several particular embodiments of the present method have been
shown and described, it will be appreciated by those skilled in the art
that changes and modifications may be made thereto without departing from
the invention in its broader aspects and as set forth in the following
claims.